FIG. 1 of the accompanying drawings corresponds to FIG. 6 of European Patent No. EP 2,475,848, the disclosure of which is incorporated by reference herein.
In FIG. 1, a valve 24 is operated by two cams 10 and 12 that act on the valve 24 by way of a summation mechanism, generally designated as 13. The summation mechanism 13 comprises a summation lever 14 having cam follower rollers 16 and 18 which respectively contact with cams 10, 12. In practice, one of the cams 12 is formed in two halves with the same profile that straddles the other cam 10. The summation lever 14 is mounted by way of a pivot pin 15 on an actuating rocker 20 of which one end contacts the tip of the valve 24 and the other end rests on a hydraulic lash adjuster 22.
The summation lever 14 is further acted upon by a control spring 30 that serves to rotate the summation lever 14 clockwise, as viewed, about its pivot pin 15 to oppose, and limit, the expansion of the hydraulic lash adjuster 22. A stop, in the form of a central rod 32, limits the expansion of the control spring 30 to set the system clearance when the cam follower rollers 16, 18 are on the base circles of their respective cams 10, 12. It should be explained that the central rod 32 contacts its stop when the control spring 30 is fully extended and this only occurs when the outer pair of cams is at its minimum lift (i.e., on the base circle). There can still be clearance in the system at other times in the cycle, such as when the central cam is on its base circle, but at that point the control spring 30 is still compressed and so the hydraulic lash adjuster 22 cannot expand as it is unable to overcome the force of the control spring 30.
In the prior art, the central rod 32 is pivotably connected at one end to the end of the summation lever 14 and at its other end it is connected to a stationary component of the engine, such as the cam cover, by an arrangement that allows the clearance to be set.
A disadvantage of the configuration in FIG. 1 is that it is difficult to assemble the valve system and to set the clearance in the system.
JP 2010 019118 describes an engine configuration intended to minimize the axial dimension of an internal combustion engine provided with a variable valve train. Camshafts and a lost motion spring are disposed in parallel in the cylinder axis direction and sub-locker arms are disposed at one side of the intake/exhaust direction of the camshafts and the lost motion spring.
DE 3725448 describes a two-armed adjusting lever (S) which is in constant contact with the running surfaces of two cams, differing in their lift and overall lift duration, and transmits the cam lifting movements by way of a pickup to the valve. Spring-loaded tappets increase the contact pressure of the adjusting lever on the cams. A rotation of the control shaft, the crank pin of which slides in the guide groove of the adjusting lever, displaces the axis of rotation of the adjusting lever and thereby adjusts the lever arm ratio between the lifting action points of the two cams and the axis of rotation. The share of the lift of each individual cam in the valve lift varies, resulting in a stepless variation of the maximum valve lift and the valve opening time. This allows the valve timing and valve timing cross-sections to be adjusted to the requirements of different engine speeds and loads in internal combustion engines.
An engine described in U.S. Pat. No. 5,373,818 comprises at least two inlet stroke valves per cylinder, the courses of the strokes of these stroke valves being adjustable in different manners. The adjustment takes place by means of an eccentric shaft which displaces the supporting point of a transfer element disposed between each cam and each stroke valve, in which case the two eccentrics assigned to one cylinder are of a different geometry. The transfer element is formed by a valve lever which is supported on the eccentric and is actuated by the cam, which valve lever, in turn, acts upon a rocker lever. The respective contact surfaces are formed by rollers. A further transfer element, which has a crank path, is also described.